1. Technical Field of the Invention
The present invention relates generally to a dilatation catheter used in angioplasty; and, more particularly, it relates to a dilatation catheter suitable for percutaneous transluminal angioplasty procedures which can perfuse blood distally of a dilatation occluding device, provide treatment of stenosis, and removal of resulting embolus.
2. State of the Prior Art
A stenosis is a narrowing or constriction of a region of a blood vessel to such a degree that blood flow is restricted. Such restrictions can be caused by a variety of restrictions, including existence of thrombus, blood clotting or deposits of cholesterol crystals, calcium, plaque, or the like. If the stenotic condition is sufficiently severe, medical treatment is required to restore adequate blood flow. These conditions can require treatment ranging from surgery under general anaesthetic for the most severe cases to angioplasty using a local anaesthetic for less severe stenotic conditions.
It is known that stenosis can occur in the arteries and, especially, the coronary arteries. In the coronary arteries, stenosis is treated by a Percutaneous Transluminal Coronary Angioplasty procedure, commonly known as PTCA, which involves percutaneous insertion of a balloon catheter to the point of stenosis. The precise point of treatment will be determined by the nature of the procedure that will be utilized. When properly located, a fluid is inserted into the balloon to cause it to expand outwardly. When placed at the point of the stenosis, the expansion outwardly under pressure causes the stenosis to be compressed against the artery wall to thereby open the artery for improved blood flow.
Many prior art balloon catheters have the disadvantages of occluding blood flow while the balloon is expanded. A number of patents describe balloon catheter structures for directly treating stenosis in this manner. Such prior art devices are not without deficiencies in the efficacy of the treatment procedure of only applying pressure to the stenosis. Blood flow stoppage for a relatively short period of time can cause damage to the portion of the vascular system or part of the heart to which the flow of blood is interrupted. An ancillary problem relates to the amount of expansion of the balloon. If expanded too far, the artery can be ruptured. Finally, while the stenosis has been compressed by the balloon, a relaxation of pressure can allow particles of the stenosis to be detached or flaked off to become free particles or embolus in the blood. If left unrecovered, such embolus can cause damage to the heart or vascular system as the embolus circulates.
A number of prior art patents have described structures to perfuse blood flow through an expanded balloon to treat stenosis. These structures allow the balloon to be expanded longer to treat the stenosis while allowing blood to flow past the occlusion. Some examples of perfusion dilatation catheters are shown in U.S. Pat. Nos. 4,581,017 to Sahota, where blood in the artery is perfused through apertures proximally and distally of the balloon; 5,279,562 to Sirhan et al., where arterial blood is perfused through a special structure to a point distal of a balloon; 5,368,566 to Crocker, where arterial blood is perfused through a reinforced structure; 4,892,519 to Songer et al., where arterial blood is perfused through proximal apertures to an interior lumen for passing through an inflatable balloon to distal apertures; 4,944,745 to Sogard et al., where arterial blood flow through a special lumen through an inflated lumen balloon to a distal port; and 5,542,925 to Orth, where arterial blood passes through specially shaped proximal ports into an interior lumen for passing through an inflated balloon to distally located shaped ports. Prior art devices use relatively complex equipment and sequences of operation to minimize damage to the vascular lumen tissue, to the downstream portions of the vascular system, and of the patient's heart.
It has been shown that complete occlusion of a vascular lumen for more than a few seconds can cause such damage. The prior art has shown systems that provide distal perfusion to minimize such damage from occluding the vascular lumen, but they too are unduly complex and require multiple structures to achieve occlusion and related treatment procedures. Further, they suffer from the major defect that embolus occurring proximally of an inflated balloon may pass downstream in the perfused flow, thereby risking damage to the vascular system or heart. This risk should be avoided. These systems also rely on the pressure of the vascular system for perfusion, and such pressure may vary to a degree that adequate perfusion for the various systems that damage may occur.